Illuminator for indicator dials



' Sept. 27, 1938. L. F. CARTER 2,131,471

' ILLUMINATOR FOR INDICATOR DIALS I v Filed April 29, 1936 NVENToR g'suePatented 27,1938

ILLUMINATOB FOR INDICATOR DIALS Leslie F. Carter, Leonla, NHL, assignorto Sperry Gyroscope Company, Inc., Brooklyn,

corporation oi New York N. Y., a

Application April 29, 1936, Serial No. 76,984

2 Claims.

This invention relates to illuminating means for indicators such asemployed on the dashboards of automobiles or the instrument panels ofaircraft. In both cases a system of indirect illumination is desirable,wherein a minimum amount of light is reflected into the eyes of theobserver, but the indications are rendered distinctly visible from thedriver's or pilots seat.

My invention is shown as applied to the form of aircraft instrumentknown as the-directional gyroscope with ball bank attachment, but it isobvious that it may be applied to many other types of instruments.

Referring to the drawing, showing one form my invention may assume,

Fig. 1 is a front elevation of such a directional gyroscope.

Fig. 2 is a vertical section through the face of the same.

Fig. 3 is a horizontal mid-section of the structure shown in Fig. l.

Fig. 4 is an enlarged sectional view through one of the lamp holders andadjacent parts.

Fig. 5 is a face view of the special glass cover for the device.

Fig. 6 is a rear elevation of the lamps and wiring therefor, theadjacent parts being shown in dotted lines.

Fig. 7 is an elementary wiring diagram of the lamp connections.

As shown, the front window of the device, or face ring I of the casing43 of the instrument is of circular shape, within which is held byspring wire I' a smaller ring shaped member 2 having an upper opening 3and a lower portion 4 having a transverse curved slot 5 therein, throughwhich the liquid ball bank indicating tube 1 and its ball 6 are visible.The directional gyro card or cards 8 and 9 are read on reference index42 and are visible through a rectangular opening in in a backgroundplate 4|. Index 42 is shown as a fine wire extending across opening 40.A glass window I0, clamped between the bezel 2 and the back plate 4i,seals the opening so that the interior of casing 43 may be made airtight.

The glass I0 is shown as circular at the top, but has a flat portion atthe bottom which lies below the upper edge 4' of part 4 of ring 2, andthe glass is cut out at opposite sides at l2 and I 3 to make 5 room forthe small illuminating bulbs I4 and I 5 which project within thesecut-out portions so as to shine the light from the miniature filamentsl6 thereof through the thickness of the glass, the direct rays towardthe dials being cut 65 off by back plate 4| (see Fig. 3). The circum-(Ci. 240-2.l)

ferential edge or periphery of the glass s ground true and provided witha reflecting interior surface as by painting it with a reflecting paint,such as white or aluminum paint, or by silvering or by frosting theperiphery, so that the rays passing through the glass in'the plane ofthe paper in Fig. 5 will strike the edge and be reflected and scatteredso that some of the rays will be deflected downwardly onto the indicatorcard or, cards. This paint covers the top H and sides l8- and I9 andouter edges 20 and 20' of the bottom, but not the output sections l2 andI3 nor the intermediate center section 2|, these sections being leftclear so that light will penetrate into the glass and a portion emergefrom 15 the glass at section 2| and illuminate the ball bank indicator.The back inner portion ll of the bezel 2 is also painted with areflecting paint,

as shown at 22 and 22', so that the rays striking the same will bereflected onto the dials. Simi- 20 larly, the rear portion of the ballbank indicating tube 1 is painted a light color, the paint beingomitted, however, from the top so that the rays from the lamp will enterthe top and illuminate the interior of the tube I and the ball 6-. All25 parts mentioned, except the markings and other graduations on thedials, are of a dull, dark color so that no more light will be reflectedinto the eyes of the observer than is necessary to see the indications.The dial graduations and numerals 30 on cards 8 and 9 and index 42 arepreferably painted with radium paint so as to increase their visibilityin dim light. The same is true of the back of tube 1.

The lamps proper are of the miniature, low 35 voltage variety such asused in surgical lamps and are shown as mounted with a slotted head 23with a threaded shank 24 adapted to be threaded in a ring 25 clamped ina hole in member 2, one wire 26 being connected to said ring. The otherwire 21 40 is shown as secured to a spring clip 28 which clamps around asmall metal thimble'29 on the base of the lamp, the filament beingconnected between the thimble and threaded base 24. Both 45 wires areshown as extending downwardly through small metal tubes 30, one wire ofone lamp being connected at its lower end to a spring pressed pin 3|,the other wire being connected to a spring pressed pin 32. Thecorresponding wires from the other lamp I5 are similarly mounted and areconnected to spring pressed pin 3| and to the same pin 32. The threepins are mounted within sockets or apertures 33 near the bottom of thebezel 2 and are normally pressed outwardly by springs '34 so that thepins engage live contacts 35 on the bottom of the window frame I.

As shown in the wiring diagram, the lamps are preferably placed inparallel, although their voltage is much below that of the normalstorage battery voltage, and a separate resistance 38, 36' provided foreach lamp so that if one lamp or resistance burns out, the other willremain lighted and will not be burned out by the sudden rise in voltage.The resistances are preferably placed in the circuit before the currentpasses into the wires on the bezel, i. e., on the supply side of thespring contacts 3|, II and 32, so that heat is not introduced near theglasscover or the indicators.

As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingshall be interpreted as illustrative and not in a limiting sense. e

Having described my invention, what I claim and desire to secure byLetters Patent is:

- 1. In an indicating instrument having an open ing therein throughwhich a main and a secondary indicator are visible, a transparent coverfor said opening having the major portion of its periphery provided withan interiorly reflecting surface to scatter light over said mainindicator but having short sections left clear, certain of said clearsections being indented and another straight, and a miniature electriclight bulb projecting beside at least one of said indented clearsections, said second indicator being at one side of the main indicatorand adjacent said straight clear section to illuminate the secondindicator.

2. In an indicating instrument having an opening therein through which amain and a secondary indicator are visible, a transparent cover for saidopening having the major portion of its periphery provided with aninteriorly reflecting surface and also having a plurality of cut outportions in its periphery, a miniature electric light bulb projectingwithin each cut out portion, the surfaces of which cut out portions aretransparent for admitting light therethrough, the light rays from thebulbs passing through the surfaces of said cutout portions into the bodyof said cover, the interiorly reflecting surfaces of said coverperiphery serving to scatterthe light'rays derived from said bulbs foreffecting indirect illumination of said main indicator, said secondaryindicator lying below said main indicator, the periphery of said coverbeing left clear adjacent thereto to illuminate the second indicator.

LESLIE F. CARTER.

